The U.S. Pat. No. 4,374,076 to Stephan et al, issued Feb. 15, 1983 and assigned to the assignee of the instant invention discloses a method for making cast precision epoxy resin bodies and an epoxy resin formulation for use therein. The epoxy resin formulation includes a two or three component system. Component A of the system consists essentially of epoxy novolac polymer, vinyl-3-cyclohexane diepoxide and 3,4 epoxy cyclohexylmethyl-3,4-epoxy cyclohexane carboxylate. Component B of the system consists essentially of a partially hydrolyzed aryl tetracarboxylic acid dianhydride, preferably partially hydrolyzed pyromellitic acid dianhydride (PMDA). In the preferred embodiments, a tertiary amine is also included in the composition. The method and epoxy resin formulation disclosed in the Stephan et al patent corrected the shrinkage which occurred during the curing of prior art epoxy resins to hardness by an additional post curing heating step causing permanent expansion of the cured solid body at least sufficient to compensate for any shrinkage during the casting and hardening thereof while in the mold.
The instant invention provides a paste anhydride for improved handling, performance, and stability in the aforementioned system.